Temp sensing acting strange all of a sudden

I suddenly started get temperature rising too slowly errors on one of my hot ends. All was fine on one print and the following print just a few minutes later had problems.

At first I thought it was a PT100 acting up, but now I think it something else. I replaced the PT100 on that hot end and the problem didn't change. However when I switch the wires to the other channel on the PT100 board it reads as expected.

Channel 1 and Channel 2 are reading the same sensor quite differently suddenly.

2 wire. They are jumped. I measured the continuity between connector screws to verify. Both PT100's measure 108.1 ohms. Channel 1 is displaying 20.8 degrees and channel 2 is displaying 15.7 degrees. I'll dig out some other resistors to verify if needed but I've reconfigured the printer to use the 'good' sensor for my primary extruder so I can get some printing done.

That's one thing I love about this board, it's easy to temporarily reconfigure this kind of stuff.